Restraint played a key role in the design of this seaside master bath. The bath belongs to a guesthouse that’s part of a Cape Cod, Mass., beach compound, and it exudes a serene, airy simplicity. “With a master bath, you’ve got to be careful you don’t overdo it,” explains project manager Kevin Dauphinais of Hutker Architects.

A glass tile floor mosaic created by interior designer Eileen Peretz and the client serves as the room’s focal point. “I wanted the tile to have a soothing effect in terms of color,” Peretz says. “That’s why we used glass.” Everything else—the surrounding white floor tiles, the freestanding tub and sink, the light-blue walls—subtly retreats to let the mosaic draw the eye. Glass doors separate the shower and the toilet from the main bath, and smaller mosaics enliven those spaces. Crisp, white-painted wainscoting ties the entire room together.

South-facing casement windows above the tub gather natural light and sea breezes. At the foot of the tub, a storage niche sits right on top of the chair rail, “so it’s almost like another window,” says principal in charge Charles Orr. The overall impression is of a bright, comfortable bath that’s received just the right amount of thought and care.